America does consist of multiple countries. Please consider that the United States acquired most of it’s territory at the expense of Native Americans¹ which are officially “domestic dependent nations”².

1: https://en.wikipedia.org/wiki/American_Indian_Wars

2: https://en.wikipedia.org/wiki/Tribal_sovereignty_in_the_Unit...

For me empire is a country that can easily project their ideology, political/economic will and military streanght outside of its boarders. And does it. For example selling cheap clothes or taxing tea and when people disagree they find their face on the reciving end of a rifle butt.